Do not copy node type in ast.Patch

Fixes #468

ast/node.go

@@ -17,7 +17,6 @@ type Node interface {
 }
 
 func Patch(node *Node, newNode Node) {
-	newNode.SetType((*node).Type())
 	newNode.SetLocation((*node).Location())
 	*node = newNode
 }

checker/checker.go

@@ -536,6 +536,14 @@ func (v *checker) SliceNode(node *ast.SliceNode) (reflect.Type, info) {
 }
 
 func (v *checker) CallNode(node *ast.CallNode) (reflect.Type, info) {
+	t, i := v.functionReturnType(node)
+	if node.Type() != nil {
+		return node.Type(), i
+	}
+	return t, i
+}
+
+func (v *checker) functionReturnType(node *ast.CallNode) (reflect.Type, info) {
 	fn, fnInfo := v.visit(node.Callee)
 
 	if fnInfo.fn != nil {

test/patch/set_type/set_type_test.go

@@ -0,0 +1,56 @@
+package set_type_test
+
+import (
+	"reflect"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/antonmedv/expr"
+	"github.com/antonmedv/expr/ast"
+)
+
+func TestPatch_SetType(t *testing.T) {
+	_, err := expr.Compile(
+		`Value + "string"`,
+		expr.Env(Env{}),
+		expr.Function(
+			"getValue",
+			func(params ...any) (any, error) {
+				return params[0].(Value).Int, nil
+			},
+			// We can set function type right here,
+			// but we want to check what SetType in
+			// getValuePatcher will take an effect.
+		),
+		expr.Patch(getValuePatcher{}),
+	)
+	require.Error(t, err)
+}
+
+type Value struct {
+	Int int
+}
+
+type Env struct {
+	Value Value
+}
+
+var valueType = reflect.TypeOf((*Value)(nil)).Elem()
+
+type getValuePatcher struct{}
+
+func (getValuePatcher) Visit(node *ast.Node) {
+	id, ok := (*node).(*ast.IdentifierNode)
+	if !ok {
+		return
+	}
+	if id.Type() == valueType {
+		newNode := &ast.CallNode{
+			Callee:    &ast.IdentifierNode{Value: "getValue"},
+			Arguments: []ast.Node{id},
+		}
+		newNode.SetType(reflect.TypeOf(0))
+		ast.Patch(node, newNode)
+	}
+}